1. Field of the Invention
The present invention relates to an image recording method, and particularly to an image recording method of recording an upper band and a lower band of a thermal head so as to overlap each other and recording record data corresponding to a plurality of dots in such a superimposition recording range in the upper and lower bands in distributed form.
2. Description of the Related Art
In general, a thermal transfer printer is often used as an output device such as a computer, a word processor or the like due to reasons such as the quality of recording, low noise, low cost, ease of maintenance, etc.
In such a commonly-used thermal transfer printer, a sheet of paper is supported forward of a platen and a carriage is equipped with a thermal head with a plurality of heating or thermal elements formed thereon. While the thermal head is being moved forward and backward alternately along the platen together with the carriage in a state in which an ink ribbon and the paper are interposed between these thermal head and platen, the ink ribbon is unreeled and the heating elements of the thermal head are selectively energized based on record information to generate heat, whereby ink of the ink ribbon is partially transferred to the paper to record an image such as desired characters or the like onto the paper.
Further, such a thermal transfer printer is accompanied by a problem that a range recorded by one scanning of the thermal head and a range recorded by the next scanning of the thermal head excessively approach each other, thereby causing a so-called black line, and the ranges are separated from each other in reverse, thereby causing a so-called white line.
In order to prevent the occurrence of such black and white lines, the range (upper band) recorded by one scanning of the thermal head and the range (lower band) recorded by the next scanning of the thermal head have heretofore been recorded so as to overlap each other.
FIG. 20 schematically shows such a conventional recording method. When the number of heating or thermal dots for the thermal head is 240 dots, for example, four dots, i.e., a 237th dot, a 238th dot, a 239th dot and a 240th dot in the upper band, and a first dot, a second dot, a third dot and a fourth dot in the lower band are recorded so as to be superimposed on one another. Further, record data corresponding to the four dots are distributed to the upper and lower bands.
In such a case, the record data have heretofore been distributed to the upper and lower bands for each one column in a superimposition recording range (corresponding to four dots) while dots in the direction of the arrangement of the respective heating elements of the thermal head (in a column direction) are being examined. Namely, when record data exist in all four dots in a first column as shown in FIG. 20, first and second two dots of the four dots are distributed to the upper band, and third and fourth two dots thereof are distributed to the lower band. In a second column, a first dot is distributed to the upper band, and third and fourth two dots are distributed to the lower band. Further, in a third column, a first dot is distributed to the upper band, and second and fourth two dots are distributed to the lower band.
Thus, the recording of data in the superimposition recording range has heretofore been carried out by suitably distributing the record data for the dots to the upper and lower bands for each column respectively and driving each individual heating element of the thermal head, based on these distributed record data.
However, the conventional thermal transfer printer is accompanied by a problem in that since the record data for the dots are distributed in each column, the quantity of record data to be processed is extremely large and a processing speed becomes slow. Therefore, when, for example, the time required to energize each heating element of the thermal head is controlled and the diameter of each recording dot is changed to thereby perform such recording as it is necessary to handle a large amount of record data as in the case of the execution of multi-tonal recording or the like, a problem arises in that the processing of record data becomes insufficient and a recording speed is reduced, thus making it impossible to perform high-speed recording.